The present invention relates to an optical composite cable which is highly flame retardant, smoke suppressed upon flaming and exhibits a reduced increase in the transmission loss.
Recently, electronic instruments such as computers and fascimiles have come into wide use. As the amount of information to be transmitted increases, the use of composite optical cable in which normal insulated electric wires of a metallic conductor and optical transmission lines of an optical fiber excellent in transmission efficiency, is growing. Wirings for the instruments are made in buildings and offices, and thus required to be flame retardant and smoke suppressed upon flaming from a view point of a prevention of calamities. Insulating materials for such wires and cables should desirably be highly flame retardant and smoke suppressed. Fluorine resins are generally used for this purpose.
With a cable of normal insulated electric wires enveloped within an outermost sheath of a fluorine resin, no problems are posed. It has been found, however, that the fluorine resin, when used as an outermost sheath of an optical composite cable having insulated electric wires and optical transmission lines enveloped within the outermost sheath, undesirably increases the transmission loss of the optical transmission lines. A particular problem relating to such optical transmission lines concerns the transmission loss, which is usually within the range between about 2 and 3 dB/Km. However, with the optical composite cable having an outermost sheath of a fluorine resin, the transmission loss of the line amounts to 1.5 to 2 times that of the optical transmission line alone. This means a reduction of the effective cable length by 1/2 to 2/3 and is a serious problem in the cable system connecting instruments.